This study was carried out in the unheated plastic greenhouses at Qaha Research Farm, Horticultural Research Institute, Qalyubia Governorate, Egypt; to evaluate the performance of a new 21 F1 squash hybrids obtained from a half diallel crosses by using seven parents at two sowing dates inside different Egyptian greenhouse conditions. Meantime, to estimate heterosis and heritability for all studied characters under different planting time inside greenhouse condition. Significant heterosis values versus mid and better parent were detected and showed highly significance for most 
studied traits. The most desirable mid and better parent heterosis values were detected for the crosses,P1 × P4, P1 × P5, P2 × P5, P3 × P5, P4 × P5 and P5×P6 for all traits under different environments. Broad sense heritability was higher than their corresponding in narrow sense heritability for all traits. Results exhibited that the recorded magnitudes of heritability in broad sense ranged from 74.89 to 99.95% for fruit traits and 94.30 to 98.45% for yield characters at different sowing date, respectively. While heritability in narrow sense ranged from 0.15% to 9.80% for fruit traits and 2.74% to 10.77% for yield characters under all environments, respectively. From the previous results, it could be 
recommended to use that the new hybrids in genetic enhancement of winter squash programme under greenhouse conditions directing to increase yield and quality traits.